NOTE: As their name suggests hints are not exactly Final Fantasy XIII-2 cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing Final Fantasy XIII-2 even more entertaining.

Achievements
Anomalous (30): Witnessed every possible Paradox Ending.
Beast Tamer (90): Befriended a most unfriendly monster.
Big Game Hunter (30): Defeated every worthy opponent.
Budding Hunter (30): Defeated an army's worth of enemies.
Cerulean Medal (14): Defeated a powerful enemy with valiant skill.
Choco-boco-holic (14): Spent a fortune at shops.
Chronosavior (90): Obtained the highest possible result in the battle to determine the fate of the world.
Clock Stopper (15): Responded swiftly to the appearance of enemies.
Defragmented (90): Completed every fragment category.
Early Riser (15): Accepted a new fate in a world where everything has changed.
Epic Finisher (90): Followed the story to its conclusion.
Fair Fighter (90): Defeated a powerful enemy on equal terms.
Fragmented (30): Completed an entire fragment category.
Future Espier (15): Visited the place where clues to the future lie waiting to be discovered.
Giant's Fist (90): Dealt 99,999 damage with a single attack.
No Retreat (16): Fought a significant number of battles without using the "Retry" option.
Obsidian Medal (14): Defeated a powerful enemy with perfect execution.
Past Gazer (15): Visited the place where the saviors of the past dream in crystal.
Promise Keeper (15): Turned your back on empty dreams and joined the battle to save mankind.Quick Draw (15): Performed a significant number of preemptive strikes.
Saddle Sore (12): Went the distance on chocobo-back.
Scarlet Medal (14): Defeated a powerful enemy with graceful poise.
Serendipitous (12): Amassed a fortune in casino coins.
Sooth Seeker (15): Prepared to face a test of your determination in the rift where hidden truths slumber.
Staggering (15): Staggered a significant number of enemies.
Strategist (18): Performed a multitude of paradigm shifts.
Supreme Being (30): Fully developed all abilities.
Threat Facer (15): Acknowledged the threat facing the world, and decided to fight back.
Time Traveler (15): Left behind a normal life, and began a journey through time.
Trigger Finger (30): Obtained five Cinematic Bonus rewards.
Wild Thing (16): Successfully used Feral Link abilities a significant number of times.

Extra items for having a FFXIII game save
Simply have a game save at any point in FFXIII while loading up FFXIII-2 to unlock these items.

Eternal Crystal: In Key Items
Lightning Mask: In treasure sphere in Serendipity, right of the entrance
Serah Mask: In treasure sphere during 3rd visit to the Void Beyond near 2nd Yeul

Improved Moggle Throw: Monster Crystals
This can only acquire when you reach Serendipity on the first time, talk to Mystic and she will give you Mog's Manifestation which can improve your moggle's throw and Haggler skill to increase your sale price by 10%. Do this moggle throw at certain areas to get one of a kind monster crystal.

Cactuarama: A Dying World 700 - Throw Mog on to position close to Chocolina in the black sands zone.
Cactuarina: New Bodhum 003AF - Throw Mog into the crater beneath the gate in the meteorite impact site area.
Chichu: Archylte Steppe ???AF - Throw Mog into the patch of red flowers close to the cactuar waystone on the plains of eternity.
Leyak: Sunleth Waterscape 300AF - Hurl Mog at the two Miniflan while riding the giant beast in the anime trail area.
Nanochu: Archylte Steppe ???AF - Throw Mog onto the small island at the center of the clearwater marshes. The probability of finding the Nanochu crystal is 10%
Rangda: New Bodhum 003AF - Throw Mog into the ocean from the pier east of the NORA house.
Silver Chocobo: Academia 4XXAF - Throw Mog onto the platform beneath the holographic projection of Cocoon.